An EMP attack is the detonation of a nuclear warhead at high altitude, causing damage similar to lightning, but much more intense and widespread. This is the most likely use of the North Korea ICBM, for these reasons:
- The accuracy requirement is reduced.
- Survival of the reentry vehicle is not an issue.
- It would cause massive damage to infrastructure. Lethality would be indirect and delayed, making it difficult to justify massive nuclear retaliation.
I have supplemented (pdf) Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack in a way specific to the North Korea threat.
Three types of EMP pulses occur:
- E1 (fast) damages most modern non-military appliances. Protection devices are typically not effective.
- E3 (slow) incurs severe damage to power distribution networks.
- E2, the intermediate pulse, is the least hazardous.
While North Korea does not appear to have warheads in the megaton range, the Soviet Alma-Ata test, conducted during the Cuban Missile Crisis on October 22, 1962, is instructive. The E1 pulse strength goes as the square root of the warhead yield. So an EMP attack is a particularly suitable use of small yield warheads.
Adjusting for altitude of the blast, the 300 kiloton Soviet yield is almost an acceptable approximation for a much smaller North Korean warhead. The difference in peak field strength would be narrowed by lower altitude. The affected area would be less, but still large.
If the warhead is designed for enhanced radiation as opposed to blast, the difference in E1 may be nil. North Korean tests of “tritium boosted” cores support this. The pdf “Nuclear weapons test effects: debunking popular exaggerations that encourage proliferation” describes the Soviet results:
The 1,000 km long Aqmola-Almaty power line was a lead-shielded cable protected against mechanical damage by spiral-wound steel tape, and buried at a depth of 90 cm in ground of conductivity 10-3S/m. It survived for 10 seconds,because the ground attenuated the high frequency field, However, it succumbed completely to the low frequency EMP at 10-90 seconds after the test, since the low frequencies penetrated through 90 cm of earth, inducing an almost direct current in the cable, that overheated and set the power supply on fire at Karaganda, destroying it. Cable circuit breakers were only activated when the current finally exceeded the design limit by 30%. This limit was designed for a brief lightning- induced pulse, not for DC lasting 10-90 seconds. By the time they finally tripped, at a 30% excess, a vast amount of DC energy had been transmitted. This overheated the transformers, which are vulnerable to short-circuit by DC. Two later 300 kt Soviet Union space tests, with similar yield but low altitudes down to 59 km, produced EMPs which damaged military generators.
It has been suggested (citation missing) that as a result of a successful, massive scale, continent-wide EMP attack, since insulin requires refrigeration, every insulin dependent diabetic in North America would die.
If you are interested in protecting some personal appliances from an EMP attack, consult your local ham radio club. Although I am unable myself to validate with authority, the FutureScience EMP pages, which I have indirectly referenced, are highly informative, and contain no obvious errors.